1. Field of Use
This invention relates generally to water pumping apparatus and systems which employ vacuum type priming pumps. In particular, it relates to electrical control systems for preventing water from overflowing from a vacuum chamber into the vacuum type priming pump.
2. Description of the Prior Art
Prior art water pumping apparatus and systems of the type to which the present invention is applicable are shown in my U.S. Pat. No. 4,029,438 entitled "Well Point Pumping System And Pump Assembly Therefor" which issued June 14, 1977. That patent discloses a well point pumping system which includes a series of well points installed in an area of the ground which is to be dewatered or dried out prior to excavation. An engine driven impeller type pump is connected for drawing water from the well points and for then discharging it elsewhere. Since the impeller type pump is usually located above the water line and since the well points pick up air as well as water, it is desirable to provide an engine operated oil-filled vacuum pump to maintain the impeller pump primed. In the prior art system, the vacuum pump is connected to a float housing which is mounted on and receives water from the housing of the impeller pump. Since entry of water from the float housing into the vacuum pump would cause loss of vacuum and possible damage to the oil-filled vacuum pump, the float housing is divided into two compartments, one of which contains a float valve which is responsive to the water level in the float chamber and operates (raises) to block the possible overflow of water from the float housing into the oil-filled vacuum pump when the water level rises to a relatively high level. The float housing also contains a normally open electric float switch to shut down the engine and stop the vacuum pump in the event the float valve fails to operate correctly. The aforedescribed float valve and the mechanical linkage associated therewith is relatively complex and costly to fabricate and install and occasionally fails to operate correctly. More specifically, in the prior art well point system using a mechanical valve, the mechanical valve creates several problems. Not only is it expense to build, but due to its weight, it is slow-acting, i.e., the water would sometimes travel faster than the valve could respond, thus allowing some water from the well point to enter into the vacuum pump system. Also due to the high cycle rate of the system, the valve and linkage tends to wear out quickly. Also, it is necessary to have float integrity, and any crack or small hole in the float would cause it to sink and become defective.